1. Field of the Invention
The present invention relates in general to a feeding device including: a drive roller that is driven by a drive source; and a driven roller that is opposed to the drive roller in its radial direction and is biased toward the drive roller, so that the drive and driven rollers cooperate with each other to feed a sheet in a feeding direction while holding the sheet therebetween. The invention also relates to an image recording apparatus equipped with such a feeding device.
2. Discussion of Related Art
A feeding device for feeding a sheet is conventionally employed in an image recording apparatus of an inkjet type such as a printer, a facsimile machine or the like. In the sheet feeding device, it is desirable to feed the sheet without deteriorating the quality of images recorded on a surface of the sheet such as a recording medium to be fed. An ordinary structure of the feeding device used on the image recording apparatus is disclosed in U.S. Pat. No. 5,961,234 (corresponding to JP-H10-167507A), for instance. Described specifically, in the disclosed feeding device, there are disposed a metallic drive roller driven by a drive source and a driven roller opposed to the drive roller in a sheet feed path through which the sheet is to be fed. The driven roller includes a plurality of rowels arranged to be opposed to a circumferential surface of the drive roller, so that the sheet can be fed, while being held by and between the drive roller and the plurality of rowels of the driven roller, with the rowels being brought into contact with a recorded surface of the sheet on which an image has been recorded. The plurality of rowels are arranged to be opposed to respective annular grooves formed in the drive roller. The drive and driven rollers are positioned relative to each other such that the rowels are received in the respective annular grooves without a toothed radially outer end portion of each rowel being brought into contact with a bottom surface of the corresponding annular groove.
In the disclosed feeding device, the driven roller including the plurality of rowels is biased by a spring, toward the drive roller, so that the sheet can be held between the drive and driven rollers during presence of the sheet therebetween. Further, with a width (axial length) of each of the annular grooves is adapted to be smaller than 10 mm, each of the rowels is displaced by a tension force of the sheet (held between the drive and driven rollers), radially outwardly toward outside the corresponding annular groove, against a biasing force generated by the spring. It is therefore possible to reduce an amount of deflection of the sheet, thereby enabling the sheet to be held in close contact with the circumferential surface of the drive roller. Still further, with the width of each of the annular grooves being adapted to be not smaller than 10 mm, the toothed radially outer end portion of each rowel is kept to be partially received in the corresponding annular groove, although each rowel is displaced by the tension force of the sheet radially outwardly toward outside the corresponding annular groove against the biasing force of the spring. Thus, a certain degree of the tension force is given to the sheet.
However, in the above-describe construction of the disclosed feeding device, during absence of the sheet between the drive and driven rollers, if each rowel is deeply received in the corresponding annular groove without its toothed radially outer end portion being in contact with any part of the annular groove, namely, if the toothed radially outer end portion of each rowel overlaps with the drive roller by a large amount, a leading end of the paper sheet, upon its entrance between the drive and driven rollers, is brought into contact with a portion of each rowel that is closed to an axis of the rowel, so that each rowel can not be smoothly rotated. Thus, the entrance of the sheet between the drive and driven rollers is made difficult, causing a risk of jamming of the sheet.
Further, upon entrance of the sheet between the drive and driven rollers, for obtaining a space available for the sheet feed path the leading end of the sheet has to force each rowel of the driven roller to be raised against the biasing force of the spring, such that each rowel is displaced outside the circumferential surface of the drive roller in the radial direction. In this instance, the biasing force of the spring acts as a force which resists the upward displacement of each rowel and increases a resistance acting against feed motion of the sheet upon entrance of the sheet between the drive and driven rollers. Such an increase in the resistance during the feed motion of the sheet is likely to cause undesirable variation in a distance by which the sheet is fed per each of the successive feed motions, causing a so-called “banding” (i.e., formation of extraneous lines in the image recorded on the sheet) and the consequent deterioration in the recording or printing quality.